The present invention relates to disk drive actuator arms used with read/write heads in computer disk drives.
A computer disk drive stores and retrieves data by positioning a magnetic read/write head over a rotating magnetic data storage disk. The head, or heads, which are typically arranged in stacks, read from or write data to concentric data tracks defined on surface of the disks which are also typically arranged in stacks. The heads are included in structures called xe2x80x9cslidersxe2x80x9d into which the read/write sensors and transducers are imbedded during fabrication. The goal in recent years is to increase the amount of data that can be stored on each hard disk. If data tracks can be made narrower, more tracks will fit on a disk surface, and more data can be stored on a given disk. The width of the tracks depends on the width of the read/write head used, and in recent years, track widths have decreased as the size of read/write heads have become progressively smaller. This decrease in track width has allowed for dramatic increases in the recording density and data storage of disks.
Hard disk drives are typically formed with an actuator arm having a gimbal assembly with the read/write head attached. The actuator arm is positioned by using a voice coil motor (VCM), and as the disks rotate, the VCM pivots the actuator arm, moving the heads over the disk surfaces. By this rotating motion, the actuator operates to position the head above the disk to read or write data on a desired track. As storage capacity of disks increases, and tracks get narrower, the task of positioning the read/write head becomes increasingly difficult, coupled with the fact that another goal is to decrease xe2x80x9cseek timexe2x80x9d or the amount of time that it takes for a read/write head to locate and position itself over a desired track.
There have been several approaches to the problems of increasing the accuracy and speed of positioning the read/write heads. A current system for positioning a read/write head over a data track employs a single stage actuator. The single stage actuator includes an actuator assembly, which pivots the actuator arm, enabling the head to read data from a particular data track. The actuator assembly typically uses the VCM alone to position the head. Disk drives with single stage actuators typically achieve a memory storage density of tens of thousands of data tracks per inch (TPI), but this density can not exceed the limit of a VCM""s precision.
In an effort to achieve finer control over the head positioning, a secondary actuator has sometimes been used with a two-stage actuator arm. A Head Stack Assembly (HSA) of the actuator arm is used as the two-stage actuator arm, and generally has a fixed portion and a movable portion, within the overall arm. The read/write head is attached to the end of the movable portion, and micro-actuators are connected between the two portions. When activated, the micro-actuator provides finer positioning adjustments to the coarser positioning provided by the VCM. These micro-actuators have used piezoelectric materials, which vary their length or shape when a voltage is applied to them. Some prior actuators have had a hinge portion connecting the fixed and movable portions, and others have had the two portions completely separated from each other with only the micro-actuators connecting them. However, this type of actuator can have problems with out-of plane movement, as the slider is caused to roll slightly. This type of motion can potentially risk damage to the disk surface, or detrimental change in fly height (spacing of head to disk). In addition to this potential out-of-plane motion, these actuators can possibly excite the load beam vibratory modes. Such excitation would limit the ability of the servo control system to achieve high bandwidth.
The data tracks are ideally symmetrical and uniform in curvature, but in practice, irregularities occur. These irregularities make it necessary for the actuators to make small adjustments in position in order for the head to remain centered on the tracks. Disks typically include servo information, which is read along with the other stored data. This servo information is sent to the control system, which then generates control signals, which help to steer the head back on track. For example, as the head encounters an irregularity in the track and begins to deviate from the track, the servo information signal can communicate this change to the control system, which then may activate a voltage to one of the micro-actuator motors to steer the head back in the direction of the track. The speed with which these irregularities can be sensed and corrected is an important factor in the proper operation of the disk drive. The number of these minute corrections, which can be achieved each second is referred to as xe2x80x9cbandwidthxe2x80x9d, and is measured in cycles per second. The greater the bandwidth, the greater the reliable operating speed of the disk drive can be, and ultimately, this allows greater storage capacity of the system.
Servo control systems generally operate better if the servo sensor and the actuator are near each other, rather than being separated in distance. The positioning of the sensor, in this case the read/write head, and the actuator in the same location is known as co-location or xe2x80x9ccollocationxe2x80x9d as the term has evolved in the industry, and collocation generally results in improved bandwidth, and faster response time.
Potential difficulties exist with collocation configurations. The actuators are desired to be as small as possible so that they do not adversely affect the performance of the drive by adding too much additional mass or bulk to the actuator arm. The face of the slider, which faces the disk is configured as an Air Bearing Surface (ABS) which has a distributed load over its face from the air pressure generated between the ABS and the spinning disk surface. This is balanced by a spring force generated through the load beam, a force, which can be as low as 30 mN (3 grams-force) or less. The performance of the actuator to move the slider as it makes its many micro-corrections of position could be adversely affected by the friction inherent in the system. The smaller the friction force to be overcome, the smaller the actuator can be, with accompanying advantages of reduced mass and volume, and thus improved performance for the disk drive, and increased practical storage capacity for the system.
FIG. 2 shows an actuator arm 2 which has an arm beam 6, which is configured in two parts which include a stationary part 12 and a movable part 14 which are connected by a narrow hinge portion 16. Two piezoelectric actuators 18 are connected between the two parts 12, 14, and act as a push-pull mechanism to direct the movable part 14. A slider 20 including a read/write head 22 is shown at the end of the movable part 14 of the actuator arm 2. A Voice Coil Motor (VCM) 9 acts as a primary actuator 7 and provides coarse positioning of the overall arm, and the piezoelectric actuators act as secondary actuators 8.
This is an example of a secondary actuator 8 in which the sensor, the read/write head 22 is separated from the actuator mechanisms 18, and thus the bandwidth is typically in the range of 1.5-3.0 kHz, which is improved compared to a bandwidth of 800-1 kHz typical for an actuator without secondary actuation, but less than that expected from a collocated actuator. In contrast, it is estimated that the bandwidth of collocated actuators is typically greater than 5 kHz.
Collocated actuators can have many configurations, but generally they include a Head Gimbal Assembly (HGA) having a load beam, and a flexure, also known as a gimbal, which is a thin springy member which functions as a leaf spring, as well as a slider containing the read/write head. Typically, actuators in the form of strips or tiny bars have been used, which have two ends, which will be referred to as the head end and the foot. In this configuration, the foot end is attached to the flexure, which acts as the stationary part and anchoring point for the actuators. The head end is attached to the slider or to a mount to which the slider is attached. When the actuators are activated by application of appropriate voltage, they deform in one of a variety of ways which serves to move the slider either laterally or laterally with some component of rotational movement with respect to the flexure. This movement is opposed by the friction generated when the upper surface of the slider rubs the lower surface of the flexure through translational movement. In addition, whenever there is frictional force which could result in abrasion of contacting surfaces, there is the possibility of freeing tiny particles, which can contaminate components. Thus, by reducing the frictional force and the contact areas involved, the risk of micro-contamination can be reduced.
Additionally, the fabrication of the HGA is made more complex when more than one actuator is used. For the sake of easy manufacturability, it is desired that the actuator configuration be as simple as possible.
Thus there is a need for a disk drive having a co-located actuator which is able to attain higher servo bandwidth than those non-collocated types of dual stage actuators and is designed for, such that friction forces on the gimbal structure during operation would be minimum.
Accordingly, it is an object of the present invention to provide an HGA for a disk drive which has co-located actuators, with associated large bandwidth.
Another object of the invention is to provide head gimbal assembly which uses shear motor actuators which provide pure or nearly pure translational movement.
Another object of the invention is to provide a design that has little to no friction in the micro actuation structure.
A further object of the present invention is to provide a HGA, which acts through pure or nearly pure translation to provide secondary collocated actuation.
An additional object of the present invention is to reduce the mass and/or volume of the HGA, and thus improve the operational dynamics of the system.
An additional object of the present invention is to reduce the micro-contamination caused by friction inside disk drives.
Briefly, one preferred embodiment of the present invention is a head gimbal assembly for a disk drive, having a load beam, a flexure, a portion of the flexure being attached to the load beam, a slider, which includes a read/write head, and a collocated microactuator, which connects between the flexure and the slider. The collocated microactuator is a shear mode piezoelectric motor for providing pure or nearly pure lateral movement to the slider, thus providing secondary actuation for the head gimbal assembly.
A disk drive including an actuator arm with the head gimbal assembly are also disclosed. The disk drive includes a servo control system which sends control signals to activate the secondary actuation of the head gimbal assembly.
An advantage of the present invention is that the present invention provides large bandwidth.
Another advantage of the present invention is that the HGA acts through pure or nearly pure translation, and moves unopposed by contact with the flexure thus providing a reduced frictional force.
And another advantage of the present invention is that a single shear motor is used which attaches between the slider and the flexure, and is thus less complex and requires less complex surrounding components than are used with multiple strip actuators.
A further advantage of the present invention is that improved dynamic performance is provided for the system.
An additional advantage is that enhanced tribology performance prevents micro-contamination. There is no friction preventing movement, mechanical hysteresis, or particulation of the material of the motor.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawings.
A multilayered piezoelectric micro-actuator is disclosed, which is embedded between a suspension flexure and a read/write slider, and which performs as a tiny electro-mechanical motor in the shear mode. When voltage is applied to the motor, it deforms laterally, causing the slider to move slightly. The small lateral motion of the slider is used with a dual-stage servo control to compensate for off-track shifts due to disk drive runouts, vibrations, thermal and other effects.